Selective transformer



Aug. 25, 19360 A. E. WOODRUFF SELECTIVE TRANSFORMER Filed Oc't. 19, 1934 FEEL? INVENTOR.

ALBERT E. WOODRUFF ATTORNEY.

' the armature.

Patented Aug. 25, 1936 UNITED STATES SELECTIVE TRANSFORMER Albert E. Woodruff, Oak Park, Ill., assignor to Associated Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application October 19, 1934, Serial No. 748,995

8 Claims.

The present invention relates generally to selective transformers or apparatus for transforming electrical: energy, but more particularly to transformers- WhiCh'Wlll respond to only a predetermined definite range of frequencies of alternating current, and-the principal object of the invention is the production of a new and improved selective transformer for passing or filtering alternating current of a predetermined frequency with very little resistancabut which is practically opaque to frequencies other than that for which the transformer is designed. 1 i

A further object of the invention is to design a transformer for the selective reception of periodic currentsignals, the frequency range of which is generally within theaudio range.

An-important feature of the invention resides inthe provision of a pair of electromagnets arranged parallel to one another, with their armatures lying in the same plane, together with means for rigidly connecting said arr-natures together.

Another feature is directed to the means for variably supporting the armature of the electromagnets.

A further feature is concerned: with the means for tuning the transformer, said means comprising adjustment of the armature supports.

The invention comprises generally a-pairoi electromagnets arranged parallel to. one another havingtheir armatures tuned to. a predetermined frequency of current. .When current. is put through the coil of one of the electroma, *,netsv it causesits armature to vibrate if the frequency is that corresponding to the resonance frequency-of The armature of the second magnet is closely coupled to. the first magnet. armatureand consequently it vibrates in. unison setting up a current flow of thesame frequency in the second magnet as existed in the first magnet. The proper. frequency ofcurrent is thereby selected. I a

selective. transformers are made use of in numerous ways, for example, in many forms of telegraphic, telephonic or electric signaling systems where a large number of alternating currentsof different frequencies are used, it is desirable to separate the different frequencies in the respective apparatus tooperate the same for certain particular purposes. Also in signaling'with a definite frequency a selective transformer may be used to exclude other frequencies and therefore eliminate interfering currents. In addition it may be used to select a definite frequency of A preferred embodiment is illustrated in the accompanying drawing in which: i

Fig. 1 shows a side View of the transformer with certain parts in section;

Fig. 2 is a top view of a, section along the line 2--2 of Fig. 1;

Fig. 3 is a section of anelectromagnet along the line 33 of Fig. 4; and

Fig. 4 is a side View section of a magnet along the line 44 of Fig. 1. r

The selective transformer comprises essential- 1y apair of electromagnetic coils indicated in the drawing as A and B, Fig. 1. They are constructed identically and a description of coil A will be deemed to be sufficient to. cover that of B as well. 15.

The unit A consists of a permanent horse-shoe magnet I between the ends of which'a pair of U-shaped pole pieces land 3 are arranged and whichhave bolts 4 and 5 on the left side and 6 and 'I' on the right side for clamping the two halves I and I I of the coilspool together and with the pole pieces- 2 and- 3 comprise; a unitary structure. A mounting plate 8 supports the units A and B by means of the bolt 9 which extends through holes in plate and the bottom leg of the permanent magnet I to a threaded ,engagement with the lower pole piece 3 The unit is thereby rigidly held-yin its proper position As seen clearly in- Figs. 1, 2 and 4 the coil itself comprises two separate halves it and II of insulating material. The upper half It is formed with a flat surface while the lower half II is arranged with a flat recess M. In addition thepart II has projections such as I2 and I3 formed on opposite sides for separating the pole pieces 2 and 3 in their clamped position. The armature I5 is rigidly suspended in the recess I4 and is free to vibrate in this space between the two halves of the coil spool as seen in Fig. 3. The coil windings 29 of the unit A are wound around the two halves Ill and I I andserve to hold them together.

An opening is formed in each end of the assembled coil 29 and spoolthrough-which the connecting rod I I extends from the right side and the supporting rod I8 from theleft side. Similar openings in the ends of the coil of unit B permit the opposite end of rod H and one end of rod 59 to extend from the spool. These openings in the coil and spools are large enough to permit free movements of the rods so they do not touch the sides of the coil or the spool. These rods including the rod IQ. of unit B may be constructed either of magnetic or non-magnetic material. One end ofrod I8 is slotted'to engage both sides of the armature I5 and is'rigidly secured to it by rivets 30. Rod I8 is likewise slotted and is rigidly secured to the opposite end of armature I5 by rivets 3I. The opposite end of rod I1 is riveted to one end of armature I8 of unit B while the rod I9 is secured to the other end of the armature. The armatures I5 and I6 therefore fioat inside the coils.

A pair of adjustable L-shaped supports 20 and 2I are arranged on opposite ends of the mounting plate 8. The support 28 at its upper end supports one end of the rod I8 together with the clamping plate 22 which by means of screws 24 clamps the rod I8 to the support 28. The other support 2I clamps rod I 9 by means of clamping plate 23 and screws 25. In order to insure that the rod I9 is always clamped tightly at two separate placesthe upper edge of the supports 20 and 2I and the bottom of the clamping plates 22 and 23 are hollowed out at 28 leaving two fairly sharp edges or surfaces around the rods I8 and I9 for clamping them. With this arrangement the supports may be shifted laterally along the rods and at any position clamped securely at two definite points. If this were not provided and the clamps and supports directly clamped to the rods along their entire surface of contact with the rods, certain unevenness in manufacture would preclude the possibility of correct adjustment and tuning of the units A and B as will presently be apparent.

The support 29 is fastened to the mounting plate 8 by means of bolt 21 threaded into the support and engaging the slot 28 in the mounting plate 8. The support 2I is similarly secured to the plate 8 by screw 32 in slot 33. The arrangement is such that by slightly loosening the bolt 21 and the screws 24 in clamping plate 22, and then moving the support 20 back and forth along rod I8, the unit A may be tuned to any desired frequency. Similarly the support 2| may be moved along rod I9 to clamp it at difierent points and tune the unit B.

In the operation of the device a source of alternating current is connected to the windings of the coil 29 of unit A. This source may comprise any number of a group of different frequencies. If the unit A is tuned to respond to a certain definite one of the frequencies the armature I5 is vibrated in resonance with that particular frequency and all others are filtered out or by passed. The vibration of armature I5 is transmitted directly to armature I6 of unit B by means of the rod I1, and this close coupling of the armatures sets up a current flow in well known manner in the coil windings of unit B which is of the same frequency as is received in the coil windings of unit A. The windings of the coil of unit B may be connected in any manner or to any desired piece of apparatus which is to be operated or controlled by the received predetermined frequency of current. The coil 29 of unit A when energized completes a magnetic circuit across the pole pieces 2 and 3 which tends to rotate the armature I5 torsionally about an axis com prising the rods I1 and I8. This torsional stress is communicated to armature I6 by rod I! to vary the magnetic flux between the pole pieces adjacent armature IS. The change in flux when the current reverses therefore causes a flow of current in the coil of unit B. The torsional suspension of the armatures I5 and I6 results, when they are vibrated, in a slight twisting of rods I8 and I9 while the rod I'I does not twist, the rods I8 and I9, however, being flexible enough so as not to effect the transmission of the vibrations from the one armature to the other.

In order to properly tune the vibrating system to any desired frequency the supports 28 and 2i are moved back and forth along the rods I8 and I9 resulting in lengthening or shortening the distance between the supports and the ends of the armatures where the rods are attached. This action as is apparent will change the free length of the rods and consequently the frequency at which the armatures I5 and I6 will be responsive. This provides a very convenient manner in which to adjust the device for any frequency. Another manner in which the device may be tuned is to provide a number of sets of rods I8 and I9 of different diameters sothat by substituting a set of rods of a certain diameter for a set of another diameter the vibrating system will respond to a different frequency. This is an obvious expedient and the effect is the same as varying the length of the rods. In all cases it should be understood that the coupling rod I'I connecting the armatures I 5 and I 8 should be relatively larger in diameter than the other rods in order to insure faithful transmission of the vibrations from armature I5 to armature I6. This coupling rod I! should also be as short as it is practical to make it in order to give close coupling between the two armatures.

An embodiment of the invention having been described, what is thought to be novel is pointed out in the appended claims.

What is claimed is:

1. In a selective transformer, a pair of electromagnets, an armature for each electromagnet, a connecting member joining said armatures together, supporting members for holding said 3 armatures in position with respect to their associated electromagnets, means for holding said sup orting members, and means for variably adjusting said holding means to variably change the tuned frequency of said armatures.

2. In a selective transformer, a pair of electromagnets, an armature for each of said electromagnets. a connecting member extending between the inner ends of said armatures, a supporting member extending from the outer ends of each of said armatures. means for ho din said supportin members. and means fo variably adjusting said holding me ns to variably change the tuned freouencv of said armatures.

3. In a selective transformer, a pa r of electroma nets each having an onening within the core. an armature posit oned with n the o ening of each elentroma net. s id electromagnets mounted para lel to one anothe a connecting member extending through said electromagnets and conmeet ng the inner ends of said armatures toget er. snnnorting me bers exte din throu h said e ectrnma nets and conn cted to the ou er ends of said arm tures for holdin said connected armatures within said elect omagnets. and an adiiistab e sunnort for each of said sunnorting m mbers for hol ing sa d supporting members at different points alo their length.

4. In a selective trans ormer. a pair of electroma nets. an. armatu e wit n ea ch el e romagnet. said electromagnets arranged parallel to one another. a connecting member co nec in the inner ed es of sa d armatures ri idly together. a supporting member extending from the outer ed es of each armatu e. an adjustable sunnort for clampin each of said supporting m mbers at different points along their length, said clamping means comprising opposing edges on said adjustable support for engaging said supporting members at only two points at a time along their length.

5. In a selective transformer for the selective reception of a particular frequency of alternating current from a source comprising a plurality of different frequencies, two electromagnets arranged parallel to one another, an armature for each of said electromagnets, a connecting member between both of said armatures and a supporting member at the ends of the armatures, said members and said armatures constituting a vibratory tuned system resonant only to a particular frequency of alternating current, one of said armatures operated responsive to the energization of its associated electromagnet by the particular frequency of current to impart a torsional stress to said members and operate said other armature in accordance with said frequency, and means responsive to the operation of said other armature for energizing its associated electromagnet with a current of the same particular frequency.

6. In a selective transformer for selecting only a particular frequency of alternating current from a source comprising a plurality of frequencies, a pair of electromagnets, a pair of armatures one for each electromagnet, a connecting member between said armatures and a supporting member at each end, said members constituting a tuned vibratory system responsive to only a particular frequency of current, one of said armatures operated by its associated electromagnet in accordance with the particular frequency to which it is responsive and through said connecting member torsionally operating said other armature, the operation of the other armature causing a current flow in the associated electromagnet correonding to the frequency received by the first electromagnet, and means on said supporting member for changing the frequency at which said vibratory system is tuned.

7. In a selective transformer, a pair of electromagnets, one of which is energized from a source of current comprising a plurality of different frequencies, an armature for each of said electromagnets, a torsional supporting arrangement for said armatures comprising a connecting member between said armatures and a supporting member at the end of each armature, said armature sup-- porting arrangement comprising a tuned vibratory system responsive to only a particular frequency of current received by said one electromagnet, the operation of said first armature by its associated electromagnet imparting a torsiona1 movement to said tuned vibratory system that is imparted to the second of said armatures, said second armature inducing a flow of current in the second electromagnet the same as is received by said first electromagnet, and means adjustably engaging said supporting members for varying the frequency at which said tuned vibratory system will respond.

8. In a selective transformer, a pair of electromagnets, an armature for each electromagnet, a torsional supporting arrangement for said armatures comprising a connecting member between both of said armatures and a supporting member on the other ends of said armatures, said members constituting a vibratory tuned arrangement with said armatures and operated torsionally about the axis of said members responsive to only a particular frequency of current flowing through one of said electromagnets, and a variable adjustable mounting for said supporting members so that the frequency with which the vibratory arrangement will respond can be altered.

ALBERT E. WOODRUFF. 

